A text index is a data structure used to facilitate full-text search over unstructured text. The structure of a text index is typically an inverted index that maps individual tokens to a list of documents that contain them. Each token and its associated list is called a posting. When users issue full-text queries, the inverted index postings are consulted to efficiently find documents that contain tokens in the queries. When documents that have been indexed are revised, the entire documents are typically completely re-indexed, which can be expensive and time-consuming.